How to setup and use Force Click on the Mac

The 2015 versions of the MacBook and 13-inch MacBook Air come with Apple's all-new Force Touch Trackpad, and that comes with Force Click.
A Force Click lets you not only click like you would on a traditional, mechanical trackpad, but press harder to engage a second click, or a range of pressure-sensitive clicks. For example, click on an icon and then Force Click to get a QuickLook, or click on a word and then Force Click to get a dictionary definition. All of this comes enabled by default on the new MacBook and on the 2015 13-inch MacBook Pro but you can toggle it off or back on in System Preferences.